High performance fiberglass composition

ABSTRACT

A glass composition is provided that includes about 55.0 to 60.4% by weight SiO2, about 19.0 to 25.0% by weight Al2O3, about 8.0 to 15.0% by weight MgO, about 7 to 12.0% by weight CaO, less than 0.5% by weight Li2O, 0.0 to about 1.0% by weight Na2O, and 0 to about 1.5% by weight TiO2. The glass composition has a fiberizing temperature of no greater than about 2,500° F. Glass fibers formed from the inventive composition may be used in applications that require high stiffness, and low weight. Such applications include woven fabrics for use in forming wind blades and aerospace structures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and any benefit of U.S. Provisional Patent Application No. 62/607,498, filed Dec. 19, 2017, the content of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Glass fibers are manufactured from various raw materials combined in specific proportions to yield a desired composition, commonly termed a “glass batch.” This glass batch may be melted in a melting apparatus and the molten glass is drawn into filaments through a bushing or orifice plate (the resultant filaments are also referred to as continuous glass fibers). A sizing composition containing lubricants, coupling agents and film-forming binder resins may then be applied to the filaments. After the sizing is applied, the fibers may be gathered into one or more strands and wound into a package or, alternatively, the fibers may be chopped while wet and collected. The collected chopped strands may then be dried and cured to form dry chopped fibers or they can be packaged in their wet condition as wet chopped fibers.

The composition of the glass batch, along with the fiberglass manufactured therefrom, is often expressed in terms of the oxides contained therein, which commonly include SiO₂, Al₂O₃, CaO, MgO, B₂O₃, Na₂O, K₂O, Fe₂O₃, TiO₂, Li₂O, and the like. Numerous types of glasses may be produced from varying the amounts of these oxides, or eliminating some of the oxides in the glass batch. Examples of such glasses that may be produced include R-glass, E-glass, S-glass, A-glass, C-glass, and ECR-glass. The glass composition controls the forming and product properties of the glass. Other characteristics of glass compositions include the raw material cost and environmental impact.

For instance, E-glass is an aluminoborosilicate glass, generally alkali-free, and commonly used in electrical applications. One advantage of E-Glass is that its liquidus temperature allows operating temperatures for producing glass fibers to be approximately 1900° F. to 2400° F. (1038° C. to 1316° C.). The ASTM classification for E-glass fiber yarns used in printed circuit boards and aerospace applications defines the composition to be 52 to 56 weight % SiO₂, 16 to 25 weight % CaO, 12 to 16 weight % Al₂O₃, 5 to 10 weight % B₂O₃, 0 to 5 weight % MgO, 0 to 2 weight % Na₂O and K₂O, 0 to 0.8 weight % TiO₂, 0.05 to 0.4 weight % Fe₂O₃ and 0 to 1.0 weight % Fluorine.

Boron-free fibers are sold under the trademark ADVANTEX® (Owens Coming, Toledo, Ohio, USA). Boron-Free fibers, such as are disclosed in U.S. Pat. No. 5,789,329, incorporated herein by reference in its entirety, offer a significant improvement in operating temperatures over boron-containing E-glass. Boron-Free glass fibers fall under the ASTM definition for E-glass fibers for use in general-use applications.

R-Glass is a family of glasses that are composed primarily of the oxides of silicon, aluminum, magnesium, and calcium with a chemical composition that produces glass fibers with a higher mechanical strength than E-Glass fibers. R-Glass has a composition that contains about 58 to about 60% by weight SiO₂, about 23.5 to about 25.5% by weight Al₂O₃, about 14 to about 17% by weight CaO plus MgO, and less than about 2% by weight of miscellaneous components. R-Glass contains more alumina and silica than E-Glass and requires higher melting and processing temperatures during fiber forming. Typically, the melting and processing temperatures for R-Glass are higher than those for E-Glass. This increase in processing temperature requires the use of a high-cost platinum-lined melter. In addition, the close proximity of the liquidus temperature to the forming temperature in R-Glass requires that the glass be fiberized at a viscosity lower than E-Glass, which is customarily fiberized at or near about 1000 poise. Fiberizing R-Glass at the customary 1000 poise viscosity would likely result in glass devitrification, which causes process interruptions and reduced productivity.

High performance glass fibers possess higher strength and stiffness, compared to traditional E-glass fibers. In particular, for some products, stiffness is crucial for modeling and performance. For example, composites, such as wind blades, prepared from glass fibers with good stiffness properties would allow for longer wind blades on electrical generating wind stations while keeping flexure of the blade within acceptable limits.

Additionally, high-performance glass compositions are desired that possess favorable mechanical and physical properties (e.g., specific modulus and tensile strength), while maintain desirable forming properties (e.g., liquidus temperature and fiberizing temperature).

In particular, there is a need in the art for high-performance glass compositions with acceptable forming properties such as having a sufficiently low fiberizing temperature, which glass compositions retain favorable mechanical and physical properties.

SUMMARY OF THE INVENTION

Various exemplary embodiments of the present inventive concepts are directed to a glass composition comprising SiO₂ in an amount from 55.0 to 60.4% by weight; Al₂O₃ in an amount from 19.0 to 25.0% by weight; CaO in an amount from 7 to 12.0% by weight; MgO in an amount from 8.0 to 15.0% by weight; Na₂O in an amount from 0 to 1.0% by weight; Li2O in an amount less than 0.5% by weight; and TiO₂ in an amount from 0.0 to 1.5% by weight, expressed as percentages by weight based on the weight of the entire composition. The weight percent ratio of Al₂O₃/MgO is less than 2.0 and glass composition has a fiberizing temperature no greater than 2,500° F.

In any of the various embodiments, the combined amounts of SiO₂, Al₂O₃, MgO, and CaO may be at least 98% by weight and less than 99.5% by weight.

In any of the various embodiments, the combined amounts of MgO and CaO may be greater than 20% by weight.

In any of the various embodiments, the combined amounts of MgO and CaO may be less than 22% by weight.

In any of the various embodiments, the glass composition may be essentially free of at least one of B₂O₃ and Li₂O.

In any of the various embodiments, the combined amounts of Fe₂O₃, TiO₂, K₂O, and Na₂O may be below 1.5% by weight.

Further exemplary aspects of the present inventive concepts are directed to a glass composition comprising SiO₂ in an amount from 55.0 to 65.0% by weight; Al₂O₃ in an amount from 19.0 to 25.0% by weight; CaO in an amount from 7 to 12.0% by weight; MgO in an amount from 8.0 to 15.0% by weight; Na₂O in an amount from 0 to 1.0% by weight; Li2O in an amount less than 0.5% by weight; and TiO₂ in an amount from 0.0 to 1.5% by weight. In various exemplary embodiments, the total weight percentage of CaO and MgO is greater than 20% by weight and the weight percent ratio of Al₂O₃/MgO is less than 2.0. The glass composition has a fiberizing temperature no greater than 2,500° F.

In any of the various embodiments, the composition comprises 19.5 to 21% by weight Al₂O₃.

In any of the various embodiments, the weight percent ratio of Al₂O₃/MgO is no greater than 1.8.

In any of the various embodiments, the glass composition may be essentially free of at least one of B₂O₃ and Li₂O.

Yet further exemplary aspects of the present inventive concepts are directed to a glass fiber formed from a glass composition comprising SiO₂ in an amount from 55.0 to 60.4% by weight; Al₂O₃ in an amount from 19.0 to 25.0% by weight; CaO in an amount from 7 to 12.0% by weight; MgO in an amount from 8.0 to 15.0% by weight; Na₂O in an amount from 0 to 1.0% by weight; Li2O in an amount less than 0.5% by weight; and TiO₂ in an amount from 0.0 to 1.5% by weight, expressed as percentages by weight based on the weight of the entire composition, wherein the weight percent ratio of Al₂O₃/MgO is less than 2.0, and wherein said glass fiber has a tensile strength of at least 4,800 MPa.

In any of the various embodiments, the weight percent ratio of Al₂O₃/MgO is no greater than 1.8.

In any of the various embodiments, the glass fiber has a specific modulus of at least 32.0 MJ/kg.

Yet further exemplary aspects of the inventive concepts are directed to a method of forming a continuous glass fiber that includes providing a molten composition according to any of the exemplary embodiments disclosed herein and drawing the molten composition through an orifice to form a continuous glass fiber.

Further exemplary aspects of the inventive concepts are directed to a reinforced composite product comprising a polymer matrix and a plurality of glass fibers formed from a glass composition comprising: SiO₂ in an amount from 55.0 to 60.4% by weight; Al₂O₃ in an amount from 19.0 to 25.0% by weight; CaO in an amount from 7 to 12.0% by weight; MgO in an amount from 8.0 to 15.0% by weight; Na₂O in an amount from 0 to 1.0% by weight; Li2O in an amount less than 0.5% by weight; and TiO₂ in an amount from 0.0 to 1.5% by weight, expressed as percentages by weight based on the weight of the entire composition, wherein the weight percent ratio of Al₂O₃/MgO is less than 2.0, and wherein said glass fibers have tensile strengths of at least 4,800 MPa.

The foregoing and other objects, features, and advantages of the invention will appear more fully hereinafter from a consideration of the detailed description that follows.

DETAILED DESCRIPTION

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which these exemplary embodiments belong. The terminology used in the description herein is for describing exemplary embodiments only and is not intended to be limiting of the exemplary embodiments. Accordingly, the general inventive concepts are not intended to be limited to the specific embodiments illustrated herein. Although other methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein.

As used in the specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Unless otherwise indicated, all numbers expressing quantities of ingredients, chemical and molecular properties, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present exemplary embodiments. At the very least each numerical parameter should be construed in light of the number of significant digits and ordinary rounding approaches.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the exemplary embodiments are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Every numerical range given throughout this specification and claims will include every narrower numerical range that falls within such broader numerical range, as if such narrower numerical ranges were all expressly written herein. Moreover, any numerical value reported in the Examples may be used to define either an upper or lower end-point of a broader compositional range disclosed herein.

The present disclosure relates to a high-performance glass composition with improved tensile strength and modulus, while being essentially lithium free. By “essentially lithium free,” it is meant that lithium is not intentionally added and the glass composition includes no greater than 5.0% by weight of lithium, including no greater than 4.0% by weight, 3.0% by weight, 2.0% by weight, 1.0% by weight, 0.5% by weight, and 0.1% by weight. In some exemplary embodiments, the glass composition includes between 0 and 1.0% by weight lithium, including between 0 and 0.5% by weight, and between 0 and 0.05% by weight. In some exemplary embodiments, the glass composition is entirely free of lithium.

The glass compositions disclosed herein are suitable for melting in traditional commercially available refractory-lined glass furnaces, which are widely used in the manufacture of glass reinforcement fibers.

The glass composition may be in molten form, obtainable by melting the components of the glass composition in a melter. The glass composition exhibits a low fiberizing temperature, which is defined as the temperature that corresponds to a melt viscosity of about 1000 Poise, as determined by ASTM C965-96(2007). Lowering the fiberizing temperature may reduce the production cost of the glass fibers because it allows for a longer bushing life and reduced energy usage necessary for melting the components of a glass composition. Therefore, the energy expelled is generally less than the energy necessary to melt many commercially available glass formulations. Such lower energy requirements may also lower the overall manufacturing costs associated with the glass composition.

For example, at a lower fiberizing temperature, a bushing may operate at a cooler temperature and therefore does not “sag” as quickly as is typically seen. “Sag” is a phenomenon that occurs when a bushing that is held at an elevated temperature for extended periods of time loses its determined stability. Thus, by lowering the fiberizing temperature, the sag rate of the bushing may be reduced and the bushing life can be maximized.

In some exemplary embodiments, the glass composition has a fiberizing temperature of less than 2,500° F., including fiberizing temperatures of no greater than 2,475° F., no greater than 2470° F., no greater than 2420° F., no greater than 2410° F., no greater than 2405° F., no greater than 2400° F., and no greater than 2390° F., and no greater than 2385° F.

Another fiberizing property of a glass composition is the liquidus temperature. The liquidus temperature is defined as the highest temperature at which equilibrium exists between liquid glass and its primary crystalline phase. The liquidus temperature, in some instances, may be measured by exposing the glass composition to a temperature gradient in a platinum-alloy boat for 16 hours (ASTM C829-81(2005)). At all temperatures above the liquidus temperature, the glass is completely molten, i.e., it is free from crystals. At temperatures below the liquidus temperature, crystals may form.

In some exemplary embodiments, the glass composition has a liquidus temperature below 2,500° F., including liquidus temperature of no greater than 2,400° F., no greater than 2,375° F., no greater than 2,350° F., no greater than 2,325° F., no greater than 2,305° F., no greater than 2,300° F., no greater than 2,290° F., no greater than 2,250° F., no greater than 2,225° F., and no greater than 2,215° F.

A third fiberizing property is “ΔT”, which is defined as the difference between the fiberizing temperature and the liquidus temperature. If the ΔT is too small, the molten glass may crystallize within the fiberizing apparatus and cause a break in the manufacturing process. Desirably, the ΔT is as large as possible for a given forming viscosity because it offers a greater degree of flexibility during fiberizing and helps to avoid devitrification both in the glass distribution system and in the fiberizing apparatus. A large ΔT additionally reduces the production cost of the glass fibers by allowing for a greater bushing life and a less sensitive forming process.

In some exemplary embodiments, the glass composition has a ΔT of at least 80 F, including at least 100° F., at least 110° F., at least 120° F., at least 135° F., at least 150° F., and at least 170° F. In various exemplary embodiments, the glass composition has a ΔT between 100° F. and 250° F., including between 120° F. and 200° F., and between 150° F. and 190° F.

An additional glass fiberizing property is the annealing temperature, which is the temperature at which the glass viscosity drops to 10¹³ Poise. Glass annealing is a controlled process of slowly cooling the glass to relieve internal stress caused during rapid cooling of glass fibers. At temperatures above the annealing temperature, the filaments begin to “sinter” and coalesce at various contact points. One of the benefits of the subject glass composition is a high annealing temperature (at least 750° C.), which allows the fibers to be used in high temperature applications, such as muffler filling. In contrast, E-glass fibers have an annealing temperature between 680 and 690° C., and boron-free E-glass fibers generally have annealing temperatures no greater than about 720° C.

The glass composition may include about 55.0 to about 65.0% by weight SiO₂, about 17.0 to about 27.0% by weight Al₂O₃, about 8.0 to about 15.0% by weight MgO, about 7.0 to about 12.0% by weight CaO, about 0.0 to about 1.0% by weight Na₂O, 0 to about 2.0% by weight TiO₂, 0 to about 2.0% by weight Fe₂O₃, and no more than 0.5% by weight Li₂O. Advantageously, the ratio of the weight percent of alumina oxide and magnesium oxide (Al₂O₃/MgO) is no greater than 2.0, such as no greater than 1.9, and no greater than 1.8. Additionally, the ratio of the weight percent of magnesium oxide to calcium oxide (MgO/CaO) is advantageously at least 1.2.

In some exemplary embodiments, the glass composition may comprise about 57.0 to about 62.0% by weight SiO₂, about 19.0 to about 25.0% by weight Al₂O₃, about 10.5 to about 14.0% by weight MgO, about 7.5 to about 10.0% by weight CaO, about 0.0 to about 0.5% by weight Na₂O, 0.2 to about 1.5% by weight TiO₂, 0 to about 1.0% by weight Fe₂O₃, and no more than 0.1% by weight Li₂O. In some exemplary embodiments, the glass composition includes an Al₂O₃/MgO ratio less than 2 and an MgO/CaO ratio of at least 1.25.

In some exemplary embodiments, the glass composition may comprise about 57.5 to about 60.0% by weight SiO₂, about 19.5 to about 21.0% by weight Al₂O₃, about 11.0 to about 13.0% by weight MgO, about 8.0 to about 9.5% by weight CaO, about 0.02 to about 0.25% by weight Na₂O, 0.5 to about 1.2% by weight TiO₂, 0 to about 0.5% by weight Fe₂O₃, and no more than 0.05% by weight Li₂O. In some exemplary embodiments, the glass composition includes an Al₂O₃/MgO no greater than 1.8 and an MgO/CaO ratio of at least 1.25.

The glass composition includes at least 55% by weight, but no greater than 65% by weight SiO₂. Including greater than 65% by weight SiO₂ causes the viscosity of the glass composition to increase to an unfavorable level. Moreover, including less than 55% by weight SiO₂ increases the liquidus temperature and the crystallization tendency. In some exemplary embodiments, the glass composition includes at least 57% by weight SiO₂, including at least 57.5% by weight, at least 58% by weight, at least 58.5% by weight, and at least 59% by weight. In some exemplary embodiments, the glass composition includes no greater than 60.5% by weight SiO₂, including no greater than 60.3% by weight, no greater than 60.2% by weight, no greater than 60% by weight, no greater than 59.8% by weight, and no greater than 59.5% by weight.

To achieve both the desired mechanical and fiberizing properties, one important aspect of the glass composition is having a Al₂O₃ concentration of at least 19.0% by weight and no greater than 27% by weight. Including greater than 27% by weight Al₂O₃ causes the glass liquidus to increase to a level above the fiberizing temperature, which results in a negative ΔT. Including less than 19% by weight Al₂O₃ forms a glass fiber with an unfavorably low modulus. In some exemplary embodiments, the glass composition includes at least 19.5% by weight Al₂O₃, including at least 19.7% by weight, at least 20% by weight, at least 20.25% by weight, and at least 20.5% by weight.

The glass composition advantageously includes at least 8.0% by weight and no greater than 15% by weight MgO. Including greater than 15% by weight MgO will cause the liquidus temperature to increase, which also increases the glass's crystallization tendency. Including less than 8.0% by weight forms a glass fiber with an unfavorably low modulus is substituted by CaO and an unfavorable increase in viscosity if substituted with SiO₂. In some exemplary embodiments, the glass composition includes at least 9.5% by weight MgO, including at least 10% by weight, at least 10.5% by weight, at least 11% by weight, at least 11.10% by weight, at least 11.25% by weight, at least 12.5% by weight, and at least 13% by weight MgO.

Another important aspect of the subject glass composition that makes it possible to achieve the desired mechanical and fiberizing properties, is having an Al₂O₃/MgO ratio of no greater than 2.0. It has been discovered that glass fibers having compositions with otherwise similar compositional ranges, but with Al₂O₃/MgO ratios greater than 2.0, are unable to achieve tensile strengths of at least 4,800 MPa. In certain exemplary aspects, the combination of an Al₂O₃ concentration of at least 19% by weight and an Al₂O₃/MgO ratio of no greater than 2, such as no greater than 1.9, and no greater than 1.85, makes it possible to obtain glass fibers with desirable fiberizing properties and tensile strengths of at least 4,800 MPa.

The glass composition advantageously includes at least 7.0% by weight and no greater than 12% by weight CaO. Including greater than 12% by weight CaO forms a glass with a low elastic modulus. Including less than 7% by weight will either unfavorably increase the liquidus temperature or viscosity depending on what the CaO is substituted with. In some exemplary embodiments, the glass composition includes at least 8.0% by weight CaO, including at least 8.3% by weight, at least 8.5% by weight, at least 8.7% by weight, and at least 9.0% by weight.

In some exemplary embodiments, the combined amounts of SiO₂, Al₂O₃, MgO, and CaO is at least 98% by weight, or at least 99% by weight, and no greater than 99.5% by weight. In some exemplary embodiments, the combined amounts of SiO₂, Al₂O₃, MgO, and CaO is between 98.3% by weight and 99.5% by weight, including between 98.5% by weight and 99.4% by weight and 98.7% by weight and 99.3% by weight.

In some exemplary embodiments, the total concentration of MgO and CaO is at least 10% by weight and no greater than 22% by weight, including between 13% by weight and 21.8% by weight and between 14% by weight and 21.5% by weight. In some exemplary embodiments, the total concentration of MgO and CaO is at least 20% by weight.

The glass composition may include up to about 2.0% by weight TiO₂. In some exemplary embodiments, the glass composition includes about 0.01% by weight to about 1.0% by weight TiO₂, including about 0.1% by weight to about 0.8% by weight and about 0.2 to about 0.7% by weight.

The glass composition may include up to about 2.0% by weight Fe₂O₃. In some exemplary embodiments, the glass composition includes about 0.01% by weight to about 1.0% by weight Fe₂O₃, including about 0.05% by weight to about 0.6% by weight and about 0.1 to about 0.5% by weight.

In some exemplary embodiments, the glass composition includes less than 2.0% by weight of the alkali metal oxides Na₂O and K₂O, including between 0 and 1.5% by weight. The glass composition may advantageously include both Na₂O and K₂O in an amount greater than 0.01% by weight of each oxide. In some exemplary embodiments, the glass composition includes about 0 to about 1% by weight Na₂O, including about 0.01 to about 0.5% by weight, about 0.03 to about 0.3% by weight, and 0.04 to about 0.1% by weight. In some exemplary embodiments, the glass composition includes about 0 to about 1% by weight K₂O, including about 0.01 to about 0.5% by weight, about 0.03 to about 0.3% by weight, and 0.04 to about 0.1% by weight.

As used herein, the terms “weight percent,” “% by weight,” “wt . %,” and “percent by weight” may be used interchangeably and are meant to denote the weight percent (or percent by weight) based on the total composition.

The inventive glass compositions may be free or substantially free of B₂O₃, Li₂O, and fluorine, although either, or any, may be added in small amounts to adjust the fiberizing and finished glass properties and will not adversely impact the properties if maintained below several percent. As used herein, substantially free of B₂O₃, Li₂O, and fluorine means that the sum of the amounts of B₂O₃, Li₂O, and fluorine present is less than 1.0% by weight of the composition. The sum of the amounts of B₂O₃, Li₂O, and fluorine present may be less than about 0.5% by weight of the composition, including less than about 0.2% by weight, less than about 0.1% by weight, and less than about 0.05% by weight.

The glass compositions may further include impurities and/or trace materials without adversely affecting the glasses or the fibers. These impurities may enter the glass as raw material impurities or may be products formed by the chemical reaction of the molten glass with furnace components. Non-limiting examples of trace materials include zinc, strontium, barium, and combinations thereof. The trace materials may be present in their oxide forms and may further include fluorine and/or chlorine. In some exemplary embodiments, the inventive glass compositions contain less than 1.0% by weight, including less than 0.5% by weight, less than 0.2% by weight, and less than 0.1% by weight of each of BaO, SrO, ZnO, ZrO₂, P₂O₅, and SO₃. Particularly, the glass composition may include less than about 5.0% by weight of BaO, SrO, ZnO, ZrO₂, P₂O₅, and/or SO₃ combined, wherein each of BaO, SrO, ZnO, ZrO₂, P₂O₅, and SO₃ if present at all, is present in an amount of less than 1.0% by weight.

As indicated above, the inventive glass compositions unexpectedly demonstrate a low fiberizing temperature and large ΔT, while providing superior elastic (Young's) modulus and tensile strength.

The fiber tensile strength is also referred herein simply as “strength.” In some exemplary embodiments, the tensile strength is measured on pristine fibers (i.e., unsized and untouched laboratory produced fibers) using an Instron tensile testing apparatus according to ASTM D2343-09. Exemplary glass fibers formed form the above described inventive glass composition may have a fiber tensile strength of at least 3,500 MPa, including at least 4,000 MPa, at least 4,500 MPa, at least 4,800 MPa, at least 4,900 MPa, at least 4,950 MPa, at least 5,000 MPa, at least 5,100 MPa, at least 5,150 MPa, and at least 5,200 MPa. In some exemplary embodiments, the glass fibers formed from the above described composition have a fiber tensile strength of from about 3500 to about 5500 MPa, including about 4000 MPa to about 5,300, about 4,600 to about 5,250 MPa. Advantageously, the combination of compositional parameters disclosed herein makes it possible to produce glass fibers having tensile strengths of at least 4,800 MPa, including at least 4,900 MPa, and at least 5,000, which has not yet been achieved by the prior art with a glass composition having desirable fiberizing properties.

The elastic modulus of a glass fiber may be determined by taking the average measurements on five single glass fibers measured in accordance with the sonic measurement procedure outlined in the report “Glass Fiber and Measuring Facilities at the U.S. Naval Ordnance Laboratory”, Report Number NOLTR 65-87, Jun. 23, 1965.

The exemplary glass fibers formed from the inventive glass composition may have a Young's modulus of at least about 85 GPa, including at least about 88 GPa, at least about 88.5 GPa, at least about 89 GPa, and at least about 89.5 GPa. In some exemplary embodiments, the exemplary glass fibers formed from the inventive glass composition have a Young's modulus of between about 85 GPa and about 95 GPa, including between about 87 GPa and about 92 GPa, and between about 88 GPa and about 91 GPa.

The modulus may then be used to determine the specific modulus. It is desirable to have a specific modulus as high as possible to achieve a lightweight composite material that adds stiffness to the final article. Specific modulus is important in applications where stiffness of the product is an important parameter, such as in wind energy and aerospace applications. As used herein, the specific modulus is calculated by the following equation:

Specific Modulus (MJ/kg)=Modulus (GPa)/Density(kg/cubic meter)

The exemplary glass fibers formed from the inventive glass composition may have a specific modulus from about 32.0 MJ/kg to about 37.0 MJ/kg, including about 33 MJ/kg to about 36 MJ/kg, and about 33.5 MJ/kg to about 35.5 MJ/kg.

The density may be measured by any method known and commonly accepted in the art, such as the Archimedes method (ASTM C693-93(2008)) on unannealed bulk glass. The glass fibers have a density of from about 2.0 to about 3.0 g/cc. In other exemplary embodiments, the glass fibers have a density of from about 2.3 to about 2.8 g/cc, including from about 2.4 to about 2.7 g/cc, and about 2.5 to about 2.65 g/cc.

In some exemplary embodiments, the glass fibers formed from the inventive glass composition have improved corrosion resistance.

According to some exemplary embodiments, a method is provided for preparing glass fibers from the glass composition described above. The glass fibers may be formed by any means known and traditionally used in the art. In some exemplary embodiments, the glass fibers are formed by obtaining raw ingredients and mixing the ingredients in the appropriate quantities to give the desired weight percentages of the final composition. The method may further include providing the inventive glass composition in molten form and drawing the molten composition through orifices in a bushing to form a glass fiber.

The components of the glass composition may be obtained from suitable ingredients or raw materials including, but not limited to, sand or pyrophyllite for SiO₂, limestone, burnt lime, wollastonite, or dolomite for CaO, kaolin, alumina or pyrophyllite for Al₂O₃, dolomite, dolomitic quicklime, brucite, enstatite, talc, burnt magnesite, or magnesite for MgO, and sodium carbonate, sodium feldspar or sodium sulfate for the Na₂O. In some exemplary embodiments, glass cullet may be used to supply one or more of the needed oxides.

The mixed batch may then be melted in a furnace or melter and the resulting molten glass is passed along a forehearth and drawn through the orifices of a bushing located at the bottom of the forehearth to form individual glass filaments. In some exemplary embodiments, the furnace or melter is a traditional refractory melter. By utilizing a refractory tank formed of refractory blocks, manufacturing costs associated with the production of glass fibers produced by the inventive composition may be reduced. In some exemplary embodiments, the bushing is a platinum alloy-based bushing. Strands of glass fibers may then be formed by gathering the individual filaments together. The fiber strands may be wound and further processed in a conventional manner suitable for the intended application.

The operating temperatures of the glass in the melter, forehearth, and bushing may be selected to appropriately adjust the viscosity of the glass, and may be maintained using suitable methods, such as control devices. The temperature at the front end of the melter may be automatically controlled to reduce or eliminate devitrification. The molten glass may then be pulled (drawn) through holes or orifices in the bottom or tip plate of the bushing to form glass fibers. In accordance with some exemplary embodiments, the streams of molten glass flowing through the bushing orifices are attenuated to filaments by winding a strand formed of a plurality of individual filaments on a forming tube mounted on a rotatable collet of a winding machine or chopped at an adaptive speed. The glass fibers of the invention are obtainable by any of the methods described herein, or any known method for forming glass fibers.

The fibers may be further processed in a conventional manner suitable for the intended application. For instance, in some exemplary embodiments, the glass fibers are sized with a sizing composition known to those of skill in the art. The sizing composition is in no way restricted, and may be any sizing composition suitable for application to glass fibers. The sized fibers may be used for reinforcing substrates such as a variety of plastics where the product's end use requires high strength and stiffness and low weight. Such applications include, but are not limited to, woven fabrics for use in forming wind blades; infrastructure, such as reinforcing concrete, bridges, etc.; and aerospace structures.

In this regard, some exemplary embodiments of the present invention include a composite material incorporating the inventive glass fibers, as described above, in combination with a hardenable matrix material. This may also be referred to herein as a reinforced composite product. The matrix material may be any suitable thermoplastic or thermoset resin known to those of skill in the art, such as, but not limited to, thermoplastics such as polyesters, polypropylene, polyamide, polyethylene terephthalate, and polybutylene, and thermoset resins such as epoxy resins, unsaturated polyesters, phenolics, vinylesters, and elastomers. These resins may be used alone or in combination. The reinforced composite product may be used for wind blade, rebar, pipe, filament winding, muffler filling, sound absorption, and the like.

In accordance with further exemplary embodiments, the invention provides a method of preparing a composite product as described above. The method may include combining at least one polymer matrix material with a plurality of glass fibers. Both the polymer matrix material and the glass fibers may be as described above.

EXAMPLES

Exemplary glass compositions according to the present invention were prepared by mixing batch components in proportioned amounts to achieve a final glass composition with the oxide weight percentages set forth in Tables 1-4, below.

The raw materials were melted in a platinum crucible in an electrically heated furnace at a temperature of 1,650° C. for 3 hours.

The fiberizing temperature was measured using a rotating cylinder method as described in ASTM C965-96(2007), entitled “Standard Practice for Measuring Viscosity of Glass Above the Softening Point,” the contents of which are incorporated by reference herein. The liquidus temperature was measured by exposing glass to a temperature gradient in a platinum-alloy boat for 16 hours, as defined in ASTM C829-81(2005), entitled “Standard Practices for Measurement of Liquidus Temperature of Glass,” the contents of which are incorporated by reference herein. Density was measured by the Archimedes method, as detailed in ASTM C693-93(2008), entitled “Standard Test Method for Density of Glass Buoyancy,” the contents of which are incorporated by reference herein.

The specific modulus was calculated by dividing the measured modulus in units of GPa by the density in units of kg/m³.

The strength was measured on pristine fibers using an Instron tensile testing apparatus according to ASTM D2343-09 entitled, “Standard Test Method for Tensile Properties of Glass Fiber Strands, Yarns, and Rovings Used in Reinforced Plastics,” the contents of which are incorporated by reference herein.

TABLE 1 Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 (% by wt.) (% by wt.) (% by wt.) (% by wt.) (% by wt.) Component SiO₂ 59.87 58.62 58.3 50.02 58.4 Al₂O₃ 21.53 21.2 21.08 21.01 21.2 MgO 9.08 10.14 10.14 10.05 10.15 CaO 7.8 8.74 8.74 8.69 8.75 Na₂O 1.5 1.07 1.5 1.0 0.30 TiO₂ 0.03 0.03 0.03 0.83 0.85 Fe₂O₃ 0.16 0.18 0.18 0.32 0.33 SiO₂/Al₂O₃ 2.78 2.77 2.77 2.76 2.75 MgO/CaO 1.16 1.16 1.16 1.16 1.16 Al₂O₃/MgO 2.37 2.09 2.08 2.09 2.09 Property Fiberizing 2502 2431 2426 2419 2418 Temperature (° F.) Liquidus 2300 2295 2309 2282 2276 Temperature (° F.) ΔT (° F.) 202 137 117 137 142 Density 2.57 2.6 2.59 2.6 2.6 (g/cc) Strength 4780 4773 4685 4692 4750 (MPa) Specific 34.2 34.2 34.2 34.2 34.3 Modulus (MJ/kg)

The glass compositions above in Table 1 (Comp. Exs. 1-5) are replicated comparative examples from European application number 10860973.6. Although these comparative examples include Al₂O₃ concentrations above 19.0% by weight, the compositions include Al₂O₃/MgO ratios above 2, which results in tensile strengths far below the minimum tensile strength of 4,800 MPa achieved by the glass fibers formed from the inventive glass compositions disclosed herein.

TABLE 2 Example 1 Example 2 Example 3 Example 4 Example 5 (X11443) (X11448) (X11449) (X11452) (X11455) (% by wt.) (% by wt.) (% by wt.) (% by wt.) (% by wt.) Component SiO₂ 59.00 59.00 58.50 59.10 59.60 Al₂O₃ 20.00 21.00 21.00 19.00 20.50 MgO 11.10 11.10 11.60 13.00 12.00 CaO 9.00 8.00 8.00 8.00 7.00 Li₂O 0.00 0.00 0.00 0.00 0.00 Fe₂O₃ 0.27 0.27 0.27 0.27 0.27 K₂O 0.07 0.07 0.07 0.07 0.07 Na₂O 0.06 0.06 0.06 0.06 0.06 TiO₂ 0.50 0.50 0.50 0.50 0.50 Al2O3/MgO 1.80 1.89 1.81 1.46 1.71 MgO/CaO 1.23 1.39 1.45 1.63 1.71 Property Fiberizing 2402 2420 2407 2375 2423 Temperature (° F.) Liquidus 2220 2293 2269 2226 2303 Temperature (° F.) ΔT 182 128 139 149 120 (° F.) Density 2.601 2.600 2.606 2.616 — (g/cc) Elastic Elastic 89.22 89.71 90.09 90.42 — Modulus (GPa) Specific 34.30 34.50 34.57 34.56 — Modulus (MJ/kg) Strength 5122 5239 5059 5119 — (MPa)

TABLE 3 Example 6 Example 7 Example 8 Example 9 Example 10 (X11456) (X11457) (X11458) (X11459) (X11460) (% by wt.) (% by wt.) (% by wt.) (% by wt.) (% by wt.) Component SiO₂ 59.10 59.10 59.10 59.10 58.70 Al₂O₃ 19.50 19.70 20.30 20.50 20.50 MgO 11.50 11.30 11.10 11.10 11.50 CaO 9.00 9.00 8.60 8.40 8.40 Li₂O 0.00 0.00 0.00 0.00 0.00 Fe₂O₃ 0.27 0.27 0.27 0.27 0.27 K₂O 0.07 0.07 0.07 0.07 0.07 Na₂O 0.06 0.06 0.06 0.06 0.06 TiO₂ 0.50 0.50 0.50 0.50 0.50 Al₂O₃/MgO 1.70 1.74 1.83 1.85 1.78 MgO/CaO 1.28 1.26 1.29 1.32 1.37 Property Fiberizing 2393 2400 2417 2413 2405 Temperature (° F.) Liquidus 2221 2218 2316 2249 2262 Temperature (° F.) ΔT (° F.) 172 182 101 164 143 Density (g/cc) 2.6060 2.6110 2.6054 2.6036 2.6108 Elastic Modulus 89.3 89.5 — — — (GPa) Specific Modulus 34.3 34.3 — — — (MJ/kg) Strength (MPa) 5004 4997 — — —

TABLE 4 Example 11 Example 12 Example 13 (X11461) (X11472) (X11505) (% by wt.) (% by wt.) (% by wt.) Component SiO₂ 59.10 58.70 59.00 Al₂O₃ 20.25 20.00 19.86 MgO 11.25 11.15 11.10 CaO 8.50 9.00 8.90 Li₂O 0.00 0.00 0.00 Fe₂O₃ 0.27 0.30 0.30 K₂O 0.07 0.07 0.07 Na₂O 0.06 0.14 0.14 TiO₂ 0.50 0.63 0.63 Al₂O₃/MgO 1.80 1.79 1.79 MgO/CaO 1.32 1.24 1.25 Property Fiberizing 2413 2390 2395 Temperature (° F.) Liquidus 2240 2214 2228 Temperature (° F.) ΔT 173 176 167 (° F.) Density 2.6059 2.612 2.6113 (g/cc) Elastic — 89.5 — Modulus (GPa) Specific — 34.3 — Modulus (MJ/kg) Strength — 4918 — (MPa)

Tables 2 to 4 illustrate the unexpected increase in tensile strength achieved by glass fibers formed from compositions comprising 55.0 to 65.0% by weight SiO₂, 19.0 to 27.0% by weight Al₂O₃, 8.0 to 15.0% by weight MgO, 7.0 to 12.0% by weight CaO, 0.0 to 1.0% by weight Na₂O, 0 to 2.0% by weight TiO₂, 0 to 2.0% by weight Fe₂O₃, and no more than 0.5% by weight Li₂O, with an Al₂O₃/MgO ratio of no greater than 2.0. It was further discovered that the unexpected increase in tensile strength is directly tied to achieving both an Al₂O₃ concentration of at least 19.0% by weight and an Al₂O₃/MgO ratio of no greater than 2.0.

Additionally, the glass compositions of Examples 1-13 have surprisingly low fiberizing temperatures (less than 2,425° F.) and large ΔT values (at least 100° F.), while achieving superior mechanical properties. Specifically, the glass fibers achieve tensile strengths of at least 4,800 MPa and specific modulus of at least 34.3 MJ/kg. Various exemplary glass fibers achieve tensile strengths of at least 4,900 MPa, or at least 4,950 MPa, or at least 5,000 MPa. Such strength and specific modulus levels are unexpected in combination with the favorable fiberizing properties.

In addition, the glass compositions are particularly suited for applications that require stiffness to be equal to or greater than R-glass (e.g., wind blades). However, as illustrated below in Table 5, the glass compositions of the present inventive concepts advantageously also have favorable fiberizing properties, such as fiberizing temperatures (less than 2,425° F.).

TABLE 5 Example 12 Comp. Example: (X11472) R-glass (% by wt.) (% by wt.) Component SiO₂ 58.70 59.00 Al₂O₃ 20.00 24.50 MgO 11.15 6.00 CaO 9.00 9.00 Li₂O 0.00 0.00 Fe₂O₃ 0.30 0.00 K₂O 0.07 0.00 Na₂O 0.14 0.00 TiO₂ 0.63 0.00 Al₂O₃/MgO 1.79 2.4 MgO/CaO 1.24 0.67 Property Fiberizing 2390 2530 Temperature (° F.) Liquidus 2214 2426 Temperature (° F.) ΔT 176 108 (° F.) Density 2.612 2.56 (g/cc) Strength 4918 5000 (MPa)

The invention of this application has been described above both generically and with regard to specific embodiments. Although the invention has been set forth in what is believed to be the preferred embodiments, a wide variety of alternatives known to those of skill in the art can be selected within the generic disclosure. The invention is not otherwise limited, except for the recitation of the claims set forth below. 

1. A glass composition comprising: SiO₂ in an amount from 55.0 to 60.4% by weight; Al₂O₃ in an amount from 19.0 to 25.0% by weight; CaO in an amount from 7 to 12.0% by weight; MgO in an amount from 8.0 to 15.0% by weight; Na₂O in an amount from 0 to 1.0% by weight; Li2O in an amount less than 0.5% by weight; and TiO₂ in an amount from 0.0 to 1.5% by weight, expressed as percentages by weight based on the weight of the entire composition, wherein the weight percent ratio of Al₂O₃/MgO is less than 2.0, and wherein said glass composition has a fiberizing temperature no greater than 2,500° F.
 2. The glass composition according to claim 1, wherein the combined amounts of SiO₂, Al₂O₃, MgO, and CaO is at least 98% by weight and less than 99.5% by weight.
 3. The glass composition according to claim 1, wherein the combined amounts of MgO and CaO is greater than 20% by weight.
 4. The glass composition according to claim 1, wherein the combined amounts of MgO and CaO is less than 22% by weight.
 5. The glass composition according to claim 1, wherein said composition comprises 19.5 to 21% by weight Al₂O₃.
 6. The glass composition according to claim 1, wherein the weight percent ratio of Al₂O₃/MgO is no greater than 1.8.
 7. The glass composition according to claim 1, wherein said composition is essentially free of B₂O₃.
 8. The glass composition according to claim 1, wherein said composition is essentially free of Li₂O.
 9. The glass composition according to claim 1, wherein the combined amounts of Fe₂O₃, TiO₂, K₂O, and Na₂O is below 1.5% by weight.
 10. A glass composition comprising: SiO₂ in an amount from 55.0 to 65.0% by weight; Al₂O₃ in an amount from 19.0 to 25.0% by weight; CaO in an amount from 7 to 12.0% by weight; MgO in an amount from 8.0 to 15.0% by weight; Na₂O in an amount from 0 to 1.0% by weight; Li2O in an amount less than 0.5% by weight; and TiO₂ in an amount from 0.0 to 1.5% by weight, wherein the total weight percentage of CaO and MgO is greater than 20% by weight and the weight percent ratio of Al₂O₃/MgO is less than 2.0, and wherein said glass composition has a fiberizing temperature no greater than 2,500° F.
 11. The glass composition according to claim 10, wherein said composition comprises 19.5 to 21% by weight Al₂O₃.
 12. The glass composition according to claim 10, wherein the weight percent ratio of Al₂O₃/MgO is no greater than 1.8.
 13. The glass composition according to claim 10, wherein said composition is essentially free of B₂O₃.
 14. The glass composition according to claim 10, wherein said composition is essentially free of Li₂O.
 15. A glass fiber formed from a glass composition comprising: SiO₂ in an amount from 55.0 to 60.4% by weight; Al₂O₃ in an amount from 19.0 to 25.0% by weight; CaO in an amount from 7 to 12.0% by weight; MgO in an amount from 8.0 to 15.0% by weight; Na₂O in an amount from 0 to 1.0% by weight; Li2O in an amount less than 0.5% by weight; and TiO₂ in an amount from 0.0 to 1.5% by weight, expressed as percentages by weight based on the weight of the entire composition, wherein the weight percent ratio of Al₂O₃/MgO is less than 2.0, and wherein said glass fiber has a tensile strength of at least 4,800 MPa.
 16. The glass fiber according to claim 15, wherein the weight percent ratio of Al₂O₃/MgO is no greater than 1.8.
 17. A glass fiber according to claim 15, wherein said glass fiber has a specific modulus of at least 32.0 MJ/kg.
 18. A method of forming a continuous glass fiber comprising: providing a molten composition according to claim 1; and drawing said molten composition through an orifice to form a continuous glass fiber.
 19. A reinforced composite product comprising; a polymer matrix; and a plurality of glass fibers formed from a glass composition comprising: SiO₂ in an amount from 55.0 to 60.4% by weight; Al₂O₃ in an amount from 19.0 to 25.0% by weight; CaO in an amount from 7 to 12.0% by weight; MgO in an amount from 8.0 to 15.0% by weight; Na₂O in an amount from 0 to 1.0% by weight; Li2O in an amount less than 0.5% by weight; and TiO₂ in an amount from 0.0 to 1.5% by weight, expressed as percentages by weight based on the weight of the entire composition, wherein the weight percent ratio of Al₂O₃/MgO is less than 2.0, and wherein said glass fibers have tensile strengths of at least 4,800 MPa.
 20. A reinforced composite product according to claim 19, wherein said reinforced composite product is in the form of a wind blade. 